Method of and device for recording information on a record carrier having a recording layer which, when heated, undergoes an optically detectable change

Abstract

Method of and device for recording information on a record carrier having a recording layer by scanning the recording layer with a radiation beam whose power has a pulsatory variation, including radiation pulses of high power, each having decreasing power, relative to and alternating with radiation intervals of low power, each having increasing power. As a result of the heat produced by the radiation pulses, the recording layer undergoes an optically detectable change. A write signal generating circuit converts an information signal into a write signal having a pulsatory pattern, including pulses of high signal values relative to and alternating with intervals of low signal values. A control circuit sets the power of the radiation beam to values fixed by the signal values of the write signal. The signal values of each of the pulses of the write signal decrease and the signal values of each of the intervals of the write signal increase. As a result, the power of the radiation beam decreases during the radiation pulses and increases during the radiation intervals, and the influence exerted by previous radiation pulses on the temperature at the scanning area is taken into account.

We claim: 
     
       1. A method of recording information on a record carrier having a recording layer in which an optically detectable change is realized by heating said layer, the method comprising: scanning said layer by means of a radiation beam having a power; and   modulating the power of said radiation beam in a pulse pattern related to the information to be recorded, said pulse pattern having pulses of high power relative to and alternating with intervals of low power, the power wherein during each of the pulses decreases and during each of the intervals increases.   
     
     
       2. The method as claimed in claim 1, wherein the power (i) decreases during each of the pulses so as to maintain a substantially uniform first temperature at a scanning area of said layer during that pulse, and (ii) increases during each of the intervals so as to maintain a substantially uniform second temperature at the scanning area of said layer during that interval, said first temperature and said second temperatures being different. 
     
     
       3. The method as claimed in claim 2, wherein said first temperature is sufficient to bring about said optically detectable change in said layer, and said second temperature is insufficient to bring about said optically detectable change in said layer. 
     
     
       4. The method as claimed in claim 1, wherein the power (i) during each of the pulses is sufficient to bring about said optically detectable change in scanning area of said layer during that pulse, and (ii) during each of the intervals is insufficient to bring about said optically detectable change in the scanning area of said layer during that interval. 
     
     
       5. The method as claimed in claim 1, wherein the power (i) during each of the pulses decreases in accordance with a first exponential function, and (ii) during each of the intervals increases in accordance with a second exponential function. 
     
     
       6. The method as claimed in claim 5, wherein said first exponential function and said second exponential function have a same time constant. 
     
     
       7. The method as claimed in claim 1, further comprising: generating a bivalent square-wave control signal for setting the power of said radiation beam;   determining an adaption signal corresponding to a measure of an influence of variation of the power on the temperature at a scanning area of said layer on the basis of said bivalent square-wave control signal;   adapting said bivalent square-wave control signal in dependence upon said adaption signal to form an adapted control signal having signal values; and   setting the power of said radiation beam to values corresponding to the signal values of said adapted control signal.   
     
     
       8. The method as claimed in claim 7, wherein said adapted control signal is determined by subtracting said adaption signal from said bivalent square-wave control signal. 
     
     
       9. The method as claimed in claim 7, wherein said adaption signal corresponds to a convolution of said bivalent square-wave control signal with a time function having a decreasing amplitude. 
     
     
       10. The method as claimed in claim 9, wherein said time function is an exponentially decreasing function. 
     
     
       11. The method as claimed in claim 7, wherein said adaption signal corresponds to a convolution of said adapted control signal and a time function having a decreasing amplitude. 
     
     
       12. The method as claimed in claim 11, wherein said time function is an exponentially decreasing function. 
     
     
       13. A device for recording information on a record carrier having a recording layer in which an optically detectable change is realized by heating said layer, the device comprising: scanning means for scanning said recording layer by means of a radiation beam having a power;   generating means for converting an information signal into a write signal of signal values having a pulse pattern having pulses of high signal values relative to and alternating with intervals of low signal values, wherein the high signal values decrease during each of the pulses and the low signal values increase during each of the intervals; and   control means for setting the power of said radiation beam to values which correspond to the high and low signal values of said write signal.   
     
     
       14. The device as claimed in claim 13, wherein said generating means comprises: conversion means for converting said information signal into a bivalent square-wave control signal;   determining means for determining an adaption signal corresponding to a measure of an influence of variation of the power on a temperature at a scanning area of said layer on the basis of said bivalent square-wave control signal; and   adaption means for adapting said bivalent square-wave control signal in dependence upon said adaption signal to form said write signal.   
     
     
       15. The device as claimed in claim 14, where said adaption means comprises means for subtracting said adaption signal from said bivalent square-wave control signal to form said write signal. 
     
     
       16. The device as claimed in claim 14, wherein said determining means comprises convolution means for convoluting said bivalent square-wave control signal and a time function with a decreasing amplitude to determine said adaption signal. 
     
     
       17. The device as claimed in claim 16, wherein said time function is an exponentially decreasing function. 
     
     
       18. The device as claimed in claim 16, wherein said convolution means comprises a low-pass filter having a pulse response which corresponds to said time function. 
     
     
       19. The device as claimed in claim 13, wherein said generating means comprises: conversion means for converting said information signal into a bivalent square-wave control signal; and   adaption means for adapting said bivalent square-wave control into said write signal.   
     
     
       20. The device as claimed in claim 19, wherein said adaption means comprises convolution means for convoluting said write signal with a time function having a decreasing amplitude to produce an adaption signal corresponding to a measure of an influence of variation of the power on a temperature at a scanning area of said layer on the basis of said bivalent square-wave signal. 
     
     
       21. The method as claimed in claim 20, wherein said time function is an exponentially decreasing function. 
     
     
       22. The device as claimed in claim 20, wherein said convolution means comprises a low-pass filter having a pulse response which corresponds to said time function. 
     
     
       23. The device as claimed in claim 22, wherein said control means sets the power of said radiation beam to values which (i) decrease in accordance with each of the pulses of said write signal and thereby maintain a substantially uniform first temperature at the scanning area of said layer for that pulse, and (ii) increase in accordance with each of the intervals of said write signal and thereby maintain a substantially uniform second temperature at the scanning area of said layer during that interval. 
     
     
       24. The device as claimed in claim 23, wherein said first temperature is sufficient to bring about said optically detectable change in said layer, and said second temperature is insufficient to bring about said optically detectable change in said layer. 
     
     
       25. The device as claimed in claim 22, wherein said control means sets the power of said radiation beam to values which (i) are sufficient to bring about said optically detectable change at the scanning area of said layer in response to each of the pulses of said write signal and (ii) are insufficient to bring about said optically detectable changes at the scanning area of said layer in response to each of the intervals of said write signal. 
     
     
       26. The device as claimed in claim 22, wherein the high signal values within each of the pulses decrease in accordance with a first exponential function, and the low signal values within each of the intervals increase in accordance with a second exponential function. 
     
     
       27. The device as claimed in claim 26, wherein said first exponential function and said second exponential function have a same time constant.